1. Field of the Invention
The present invention relates to a liquid delivery device which delivers liquid. More particularly, it relates to a solvent delivery device which delivers eluent in an analytical system such as a liquid chromatograph.
2. Description of the Related Art
In liquid chromatography, it is ideal that a solvent delivery device always deliver eluent at a constant flow rate. If the flow rate is not constant, the analysis accuracy is lowered. However, it is common that the rate of flow from a solvent delivery device periodically changes (hereinafter this phenomenon being termed pulsation).
An example of the prior art techniques intended to reduce pulsations is described in Japanese Patent No. 3709409. However, this technique might face a problem if applied to a solvent delivery device in such an analytical system as a liquid chromatograph where solvent must be delivered at very high pressure. Specifically, this is because providing a pressure sensor increases the volume of eluent to be compressed. If this volume is so large that the eluent cannot fully be compressed, it may be impossible to deliver the eluent at a constant flow rate. Here, “very high pressure” means such a high pressure that the eluent is considerably compressed at the pressure. For example, if the eluent is methanol and delivered at 60 MPa, the methanol reduces 6.4% in volume as compared with its volume before compressed.
In a solvent delivery device disclosed in JP-A-2001-254683, a load sensor is used to reduce the volume of eluent to be compressed and the volume of eluent to be compressed is small. However, this does not contribute to reducing pulsations since the quantity of load measured by the load sensor is not related to the pressure of the eluent.